1. Field of the Invention
The present invention relates to a piezoelectric bimorph type actuator, in particular, a piezoelectric bimorph type actuator suitable for use in the shutter mechanism of a camera.
2. Description of the Related Art
Piezoelectric bimorph type actuators of the type contemplated by the present invention have a piezoelectric plate provided on both sides of an electrode plate. In a typical case, one end of the actuator is cantilevered while the other end thereof is permitted to move freely. With this arrangement, a voltage is applied between each piezoelectric plate and the electrode plate so as to displace the free end. This displacement is typically used to drive a mechanism such as the shutter mechanism of a camera.
The displacement of conventional actuators can be increased by applying an increased voltage. One may readily figure out that in order to provide a sufficient stroke to drive the shutter mechanism of a camera under a constant voltage, it is necessary to extend the free end or reduce its thickness. However, the result of this approach is that the force (of displacement) generated at the free end is insufficient to drive the shutter mechanism.
Thus, in order to produce the necessary stroke while generating a desired force of displacement, the above-described approach may be combined with increasing the dimension of the actuator in the direction of width. In this case, however, the actuator size becomes bulky, potentially causing inconveniences when incorporating it into the camera which is a small device.
A further problem with the conventional approach of increasing the displacement of an actuator by extending its free end or reducing its thickness is that the resonant frequency (natural frequency) of the actuator decreases resulting in potential deterioration in its operation.